I think that the NTSB investigation should continue and parallel the FBI investigation.
The NTSB should be the ones deciding if the wreckage supports a deliberate act as well.
eye witness reports ( typically not reliable by itself) that they hear the engine sound go quiet and looked up to see the wings wobble and then the plane fell of into a dive. It was on approach over P&W to an airport across the river.
If it was intentional it was way too late after having passed over P&W